Abstract
AbstractAn exceedingly small number of high‐pressure polymorphs have been discovered in lunar samples. This situation does not seem to reconcile with the prolonged, intense bombardment of the lunar surface, which should produce suitable conditions for the formation of such polymorphs. Here we report the discovery of reidite, a high‐pressure polymorph of ZrSiO4 with scheelite structure in lunar meteorite Sayh al Uhaymir (SaU) 169. The reidite occurs mainly as lamellae hosted within zircon, likely corresponding to a deviatoric‐dominated transformation. The presence of reidite in the regolith portion of SaU 169 indicates a narrow temperature and pressure path constrained by the phase stability under low pressure and suggests heterogeneous shock features in the porous lunar regolith where the ambient temperature increases much higher than that in compact rocks. The inventory of high‐pressure polymorphs might be restricted by such unusual cooling processes lunar samples experienced.
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